Biology subjects

Diaz, C. G.

Publications and source records attributed to Diaz, C. G..

3 recordsLinked to original sources

bioRxiv2022

Elevated FOXG1 supports exit from quiescence in neural stem cells through FoxO6

The molecular mechanisms controlling the balance of quiescence and proliferation in adult neural stem cells (NSCs) are often deregulated in brain cancers such as glioblastoma (GBM). Previously, we reported that FOXG1, a forebrain-restricted neurodevelopmental transcription factor, is frequently upregulated in glioblastoma stem cells (GSCs) and limits the effects of cytostatic pathways, in part by repression of the tumour suppressor Foxo3. Here, we show that increased FOXG1 upregulates FoxO6, a more recently discovered FoxO family member with potential oncogenic functions. Although genetic ablation of FoxO6 in proliferating NSCs has no effect on the cell cycle or entry into quiescence, we find that FoxO6-null NSCs can no longer efficiently exit quiescence following FOXG1 elevation. Increased FoxO6 results in the formation of large acidic vacuoles, reminiscent of Pak1-regulated macropinocytosis. Consistently, Pak1 expression is upregulated by FOXG1 overexpression and downregulated upon FoxO6 loss in proliferative NSCs. These data suggest a pro-oncogenic role for FoxO6 in controlling the exit from quiescence in NSCs, and shed light on the functions of this underexplored FoxO family member. Research highlightsO_LIFoxO6 is a downstream effector of elevated FOXG1 in mouse NSCs and GSCs. C_LIO_LIUpregulation of FoxO6 is necessary for FOXG1 to drive efficient quiescence exit of NSCs. C_LIO_LIFoxO6 overexpression stimulates macropinocytosis, a process regulated by the actin cytoskeleton regulator Pak1. C_LIO_LIPak1 is upregulated by FOXG1 overexpression and downregulated upon FoxO6 loss. C_LI

cancer biology↗

bioRxiv2020

The linear ubiquitin chain assembly complex generates heterotypic ubiquitin chains

The linear ubiquitin chain assembly complex (LUBAC) is the only known ubiquitin ligase that generates linear/Met1-linked ubiquitin chains. One of the LUBAC components, HOIL-1L, was recently shown to catalyse oxyester bond formation between the C-terminus of ubiquitin and some substrates. However, oxyester bond formation in the context of LUBAC has not been directly observed. We present the first 3D reconstruction of LUBAC obtained by electron microscopy and report its generation of heterotypic ubiquitin chains containing linear linkages with oxyester-linked branches. We found that addition of the oxyester-bound branches depends on HOIL-1L catalytic activity. We suggest a coordinated ubiquitin relay mechanism between the HOIP and HOIL-1L ligases supported by cross-linking mass spectrometry data, which show proximity between the catalytic RBR domains. Mutations in the linear ubiquitin chain-binding NZF domain of HOIL-1L reduces chain branching confirming its role in the process. In cells, these heterotypic chains were induced by TNF. In conclusion, we demonstrate that LUBAC assembles heterotypic ubiquitin chains with linear and oxyester-linked branches by the concerted action of HOIP and HOIL-1L.

biochemistry↗

bioRxiv2018

The anti-apoptosis ubiquitin E3 ligase XIAP promotes autophagosome-lysosome fusion during autophagy

The Inhibitor of Apoptosis Protein (IAP) family members are well-known endogenous regulators of apoptosis. Whether these proteins regulate other degradation pathways is unclear. Here, we discovered that the IAP member X-linked IAP (XIAP) is crucial for macroautophagy. Loss of XIAP in mouse and human cells inhibited starvation-induced degradation of LC3 proteins and an autophagy substrate p62. It also led to the accumulation of mature autophagosomes, suggesting that XIAP controls autophagic flux by mediating autolysosome formation. Xiap{triangleup}RING/{triangleup}RING cells phenocopy the autophagy defects of Xiap-/- cells, suggesting that the ubiquitinating activity mediated by the catalytic RING domain is critical for autophagic flux. We found that XIAP physically interacts with Syntaxin 17, a regulator of autophagosome-lysosome fusion. Syntaxin 17-positive mature autophagosomes positive accumulate in the cytoplasm of starved Xiap-/- cells, suggesting that XIAP might regulate its dissociation from autophagosomes after fusion. XIAP selectively interacts with GABARAP among LC3 family members via the LIR-Docking Site (LDS). Together, our data suggest that XIAP-mediated ubiquitination regulates key autophagy regulators to promote autophagosome-lysosome fusion.

cell biology↗